摘要:

Two novel aliphatic polyurethaneurea anionomers were synthesized based on polydimethylsiloxane (PDMS)-polytetramethylene oxide (PTMO) soft segments. The hard segments consisted of either 4,4'-methylene dicyclohexyl diisocyanate (H12MDI), sulfonic acid-containing diol and 1,4-butandiol (BD) or H12MDI, carboxylic acid-containing diol and BD. The nonionic counterpart chain extended with BD was prepared. In addition, the base nonionic polyurethaneurea containing a pure PDMS soft segment, which is denote H-D-BD, was also studied for comparison. The effects of soft segment type and ion incorporation on the physical properties, surface properties, and plateled adhesion are discussed. The ionic polyurethaneureas exhibited poor phase separation, a smaller fraction of PTMO present at the surface, and a smaller contact angle. On the other hand, it also showed a larger fraction of PDMS present at the surface and a higher water absorption value than its nonionic counterpart. H-D-BD had more phase-separated structure, a larger fraction of PDMS present at the surface, and larger contact angle but lower water absorption value than the PTMO-containing polyurethaneureas. The in vitro platelet adhesion experiments indicated that the ionic groups, especially for carboxylate, and surface enrichment PDMS soft segment could effectively inhibit platelet adhesion.

ISSN:0920-5063    

DOI:10.1163/156856299X00018

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The ability of Staphylococcus to recognize several extracellular matrix or plasma proteins (e.g., fibrinogen, fibronectin, and collagen) promotes bacterial attachment to artificial surfaces. Whereas most S. aureus clinical isolates elaborate a wide repertoire of bacterial surface 'receptors' called adhesins, exhibiting specific binding of individual host proteins, S. epidermidis is lacking most of such protein adhesins. To document the interactions between S. epidermidis and various surface-adsorbed proteins, we first compared promotion of bacterial attachment by seven purified human proteins immobilized onto poly(methyl methacrylate) (PMMA) coverslips. Only two of them, namely fibronectin and fibrinogen, exhibited adhesion-promoting activities. In the presence of native heparin or two functionalized dextrans (CMDBS for Carboxy Methyl, Benzylamide sulfonate/sulfate), a dose-dependent inhibition of S. epidermidis adhesion to fibronectin-coated, but not to fibrinogen-coated surfaces was observed. The inhibitory effects of each CMDBS were much stronger than that of native heparin. In contrast, a control highly negatively charged dextran exclusively substituted with carboxy methyl groups exerted no inhibition on S. epidermidis adhesion. To evaluate how CMDBS could interfere with S. epidermidis attachment to coverslips coated in vivo with extracellular matrix components, we also tested PMMA surfaces retrieved from tissue cages Subcutaneously implanted in guinea pigs. Each CMDBS, but not heparin, strongly inhibited S. epidermidis adhesion to explanted coverslips, even in the presence of tissue cage fluid. In conclusion, fibronectin plays an important role in promoting S. epidermidis attachment to implanted biomaterials. Furthermore, S. epidermidis adhesion to fibronectin-coated or implanted biomaterials can be efficiently blocked in vitro by CMDBS.

ISSN:0920-5063    

DOI:10.1163/156856299X00027

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Immobilization of invertase in thiophene-capped poly(methylmethacrylate)/polypyrrole matrices was achieved by constant potential electrolysis using different supporting electrolytes. Optimum reaction conditions such as substrate concentration, temperature, and pH for the enzyme electrodes were determined. The temperature and pH were found to be 60°C and 4.8, respectively. The effect of supporting electrolyte on the enzyme activity revealed that SDS was the best in the immobilization procedure. Michaelis-Menten constant and the maximum reaction rate in PMMA/PPy matrices were of the order of that of pristine polypyrrole. However, in terms of repeated use, the copolymer matrices were superior to polypyrrole.

ISSN:0920-5063    

DOI:10.1163/156856299X00036

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

For development of bio-reactor enzymes stimuli-responsive polymers have been employed as immobilizing matrices. The stimuli-responsive polymers have been used for solubility control in water. Recently we first succeeded in the solubility control in organic media by conjugation with photo-responsive polymer. The polymer-conjugated enzymes can efficiently catalyze various chemical reactions in the soluble state and can be recovered by precipitation in response to the stimulation. In this review, the conjugation method and recent progress is described.

ISSN:0920-5063    

DOI:10.1163/156856299X00045

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Multi-layered hydrogel formulations consisting of poly(ethylene glycol)-grafted dextran (PEG-g-Dex) and ungrafted Dex were investigated as a model of Pulsatile drug release. In these formulations, it is considered that the grafted PEG domains act as a drug reservoir dispersed in the Dex matrix based on aqueous polymer two-phase systems. The formulations exhibited surface-controlled degradation by dextranase, and insulin release was observed in a pulsatile manner because of the multi-layered structure, PEG-g-Dex hydrogel layers containing insulin and insulin-free Dex hydrogel layers. Thus, it is suggested that the multi-layered hydrogel formulations using PEG-g-Dex and Dex are feasible for chronopharmacological drug delivery systems.

ISSN:0920-5063    

DOI:10.1163/156856299X00054

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Studies have shown that monomers from dental resins are acutely cytotoxic, but little is known of their long-term effects at sub-lethal concentrations. The current study determined the long-term effects of sub-lethal concentrations of TEGDMA (triethyleneglycol dimethacrylate) and Bis-GMA (bisphenol-glycidylmethacrylate), two common dental monomers, on the in vitro cellular proliferation, succinic dehydrogenase activity, and total cellular protein production of monocytes. Human THP-1 monocytes were exposed to concentrations of 100, 200, and 400 μmol l-1of TEGDMA or 1, 5, and 25 μmol l-1Bis-GMA for 5 weeks. Controls received only vehicle solutions of ethanol. Each week cellular proliferation (hemocytometer), succinic dehydrogenase (SDH) activity (MTT) and total cellular protein (bicinchoninic acid) were assessed. The results were compared with ANOVA and Tukey intervals (α =0.05). TEDGMA had no proliferative or cellular protein effects, but increased SDH activity 20-60% in week 1 (p < 0.05). SDH activity then decreased 40% in week 2, followed by a gradual increase of 30-40% over week 3-5 (p < 0.05). Bis-GMA reduced proliferation by 40-60% from 1-5 weeks exposure (p < 0.05). However, SDH activity and total protein per cell were not affected. There was some indication of increased SDH activity after 5 weeks (20-30%, p < 0.05). Sub-lethal concentrations of TEGDMA and Bis-GMA have significant long-term effects on monocytes at low-dose 5-week exposures in vitro. Each monomer acted differently.

ISSN:0920-5063    

DOI:10.1163/156856299X00063

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Acetylation of biodegradable polyrotaxanes was examined to estimate the effect on its supramolecular dissociation via terminal ester hydrolysis. The biodegradable polyrotaxanes, in which many α-cyclodextrins (α-CD) are threaded onto a poly(ethylene glycol) chain capped with L-phenylalanine via ester linkages, were acetylated using acetic anhydride; α-CD release behavior was then characterized by in vitro hydrolysis. The degree of acetylation was changed by the concentration of acetic anhydride and the reaction time. The results of the in vitro hydrolysis indicate that the critical degree of acetylation to prolong supramolecular dissociation lies at around 30%. The terminal hydrolysis proceeded completely even with 100% of acetylation. These findings suggest that the hydrophobization of α-CDs in the polyrotaxane makes it possible to delay the time to complete the supramolecular dissociation. The hydrophobization of the polyrotaxane is of great importance for designing implantable materials that maintain their supramolecular structure until tissue regeneration with complete terminal hydrolysis.

ISSN:0920-5063    

DOI:10.1163/156856299X00072

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Attenuated total reflectance infrared spectroscopy was used to investigate possible interactions during transport of oxprenolol . HCl, bovine serum albumin, α-chymotrypsin, and fibrinogen through poly(acrylic acid) and its random copolymeric gels. Carbonyl and carboxylate ion peak shifts were used to identify drug/gel binding due to electrostatic and hydrogen bond interactions between the polymer carrier and the drugs tested. These findings were used to interpret the decrease in calculated diffusion coefficients of drugs diffusing through these gels and the associated hindering of drug transport. A model was developed to analyze this transport process as a function of the binding heat of the drug with the polymer.

ISSN:0920-5063    

DOI:10.1163/156856299X00081

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor